GDF-5 is a member of the Bone Morphogenetic Proteins (BMP), which is a subclass of the TGF-β superfamily of proteins. GDF-5 includes several variants and mutants, including mGDF-5 first isolated from the mouse by Lee (U.S. Pat. No. 5,801,014). Other variants include MP52, which is the patented name (WO 95/04819) for the human form of GDF-5, which is also known as hGDF-5 and also as LAP-4 (Triantfilou, et al. Nature Immunology 2, 338-345 (2001)); also CDMP-1, an allelic protein variant of hGDF-5 (WO 96/14335); also rhGDF-5, the recombinant human form manufactured in bacteria (EP 0955313); also rhGDF-5-Ala83, a monomeric variant of rhGDF-5; also BMP-14, a collective term for hGDF-5/CDMP-1 like proteins; also Radotermin, the international non-proprietary name designated by the World Health Organization; also HMW MP52's, high molecular weight protein variants of MP52; also C465A, a monomeric version wherein the cysteine residue responsible for the intermolecular cross-link is substituted with alanine; also other active monomers and single amino acid substitution mutants including N445T, L441 P, R438L, and R438K. For the purposes of this applciation the term “GDF-5” is meant to include all variants and mutants of the GDF-5 protein, and rhGDF-5 is the exemplary member having 119 amino acids.
All members of the BMP family share common structural features including a carboxy terminal active domain and share a highly conserved pattern of cysteine residues that create 3 intramolecular disulfide bonds and one intermolecular disulfide bond. The active form can be either a disulfide-bonded homodimer of a single family member or a heterodimer of two different members (see Massague, et al. Annual Review of Cell Biology 6:957 (1990); Sampath, et al. Journal of Biological Chemistry 265:13198 (1990); Celeste et al. PNAS 87:9843-47 (1990); U.S. Pat. No. 5,011,691, and U.S. Pat. No. 5,266,683). The proper folding of the GDF-5 protein and formation of these disulfide bonds are essential to biological functioning, and misfolding leads to inactive aggregates and cleaved fragments.
The production of BMP's from genetically modified bacteria, and of GDF-5 in particular, utilizes plasmid vectors to transform E. coli to produce monomer GDF-5 protein in high yield (see for example Hotten U.S. Pat. No. 6,764,994 and Makishima U.S. Pat. No. 7,235,527). The monomer is obtained from inclusion bodies, purified, and refolded into homodimers of GDF-5 protein to produce the biologically active dimer of the GDF-5 protein. The steps leading to this utilize various pharmaceutically unacceptable materials to modify the solubility in order to enable the separation and purification of the GDF-5 protein.
The degradation of proteins in general has been well described in the literature, but the storage and solubility of bone morphogenetic proteins, particularly GDF-5 has not been well described. BMP-2 is readily soluble at concentrations greater than 1 mg/ml when the pH is below 6, and above pH 6 the solubility can be increased by the addition of 1 M NaCl, 30% isopropanol, or 0.1 mM heparin (Ruppert, et al Eur J Biochem 237, 295-302 (1996). The solubility of GDF-5 is much more limited than that of BMP-2, and GDF-5 is nearly insoluble in physiological pH ranges and buffers. GDF-5 is only soluble in water at extreme pH (Honda, et al, Journal of Bioscience and Bioengineering 89(6), 582-589 (2000)). GDF-5 is soluble at an alkaline pH of about 9.5 to 12.0, however proteins degrade quickly under these conditions and thus acidic conditions are used for preparation of GDF-5 protein.
The use of bone morphogenetic proteins has been well described in the case of BMP-2 and the growth of bone. GDF-5 has more activity in other areas of musculoskeletal development than BMP-2, and indeed in other areas of cellular biochemistry and regulation. The use of GDF-5 in these other areas presents fertile ground for potential treatments of various diseases and medical conditions. A major challenge for storage, handling, and delivery to target tissues is the stability of the GDF-5 protein molecule. Bulk GDF-5 protein is typically stored at sub-zero temperatures and lyophilized products are stored at 2-8C to protect the protein from degradation, but liquid formulations are required for many uses, including delivering liquid product in an implantable drug delivery pump.
In the past we have shown that a high amount of excipient, such as 60% trehalose, could be used to protect the GDF-5 protein at body temperature for extended periods of time. These formulas however were not isotonic and must be diluted before reaching the injection site. Biocompatible formulations of the GDF-5 protein present great challenges to obtain reasonable solubility and concurrent stability of the GDF-5 protein. Thus there is a need for improved formulations for the storage, handling, and delivery of GDF-5 protein solutions.